SMTA International Conference Proceedings

Analysis of the Root Cause for Solder Joint Cracking

Authors: Chaohui Hu, P.E., Weiming Li, P.E., Jianghua Shen, P.E.
Company: China CEPREI Laboratory
Date Published: 9/22/2019   Conference: SMTA International

Abstract: The Insulated Gate Bipolar Transistor (IGBT) on the control board of a certain type of industrial equipment has been burned out. Through the investigation and analysis of IGBT device and its circuit, it is confirmed that there is no abnormality in the device itself, and the burnout is due to the cracking of solder joint. The microsection morphology observation of similar solder joints showed that fatigue cracking occurs in solder joints, and there were micro-cracks in some unused solder joints. With the help of real-time strain monitoring, it was found that the strain of IGBT solder joints was extremely high during the process of product ex-factory testing and operation, which easily lead to solder joint damage. Finally, Vibration simulation analysis of solder joint in practical application shows that the position of IGBT pin was the stress concentration point, and the stress of pin in failure board is higher than that of pins in other types of board.

The process of inserting for testing in the factory would cause great stress on IGBT solder joints, which could easily lead to micro-cracks in the solder joints. The simulation analysis confirmed that the position of IGBT pin was the stress concentration point under typical vibration conditions, and the stress fatigue crack continued to expand during the working process. IGBT device pins were heated by high current, and the increase of resistance caused by solder joint cracking further improves the heating power of solder joints and further promotes the fatigue cracking of solder joints. Under the coupling effect of vibration stress and thermal stress, cracks gradually penetrated through the solder joints, and ultimately lead to cracking failure of the solder joints.

Key Words: 

solder joint, cracking, failure analysis

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